Cobalt iron magnetic alloys

ABSTRACT

THE STRENGTH OF COBALT-IRON MAGNETIC ALLOYS IS IMPROVED BY THE PRESENCE OF SECONDARY PHASE PARTICLES WITH RETENTION OF GOOD MAGNETIC PROPERTIES.

United States Patent, ce

Patented Aug. 17, 1971 3,600,162 COBALT IRON MAGNETIC ALLOYS Asa Kaplan, Ballston Lake, and Robert F. Gill, Schenectady, N.Y., assignors to General Electric Company No Drawing. Filed Aug. 29, 1968, Ser. No. 756,308 Int. Cl. C22c 39/14 US. Cl. 75-126C 6 Claims ABSTRACT OF THE DISCLOSURE The strength of cobalt-iron magnetic alloys is improved by the presence of secondary phase particles with retention of good magnetic properties.

This invention relates to magnetic cobalt-iron magnetic alloys. More particularly, it relates to new and useful alloys of the above type which are possessed of the magnetic qualities usual in such materials but which at the same time are mechanically strong for operation at elevated temperatures.

With the development of equipment, including compact electrodynamic machinery, such as generators and motors, which, because of their design operate at temperatures at and over 1000 F. and often of the order of 1200 F. to 1400 F., there has developed a corresponding problem of providing so-called soft magnetic materials which will have relatively high strength at such temperatures. While cobalt-iron alloys are capable of providing the magnetic properties required in such installations, they are not normally possessed at such temperatures of the high strength often required. Generally speaking, good magnetic quality and high strength are not compatible, particularly if the strengthening mechanism involves modification of the matrix as in the formation of martensite for strengthening purposes, it being well known that magnetic quality is an inverse function of the hardness and quantity of martensite present; Thus, while cobalt-iron alloys have good magnetic characteristics at elevated temperatures, they are lacking in the high strength which is also often required for such operation. It is accordingly a primary object of this invention to provide cobalt-iron alloys which will not only have good magnetic qualities but at the same time have a strength which is commensurate with their use in electrodynamic machinery and other equipment operating at elevated temperatures.

It has been found according to the present invention that soft magnetic cobalt-iron alloys can be suitably strengthened for high temperature operation with retention of good magnetic qualities by secondary phase hardening with metallic carbide particles or equivalent particles which are distributed through the matrix of the alloy Without modifying the matrix itself. Among the carbide formers which can be used in connection with the invention are niobium (columbium), titanium, tantalum, and other suitable Group IV, V elements.

Generally speaking, the alloys of the present invention contain in percent by weight from 0.005 to 0.6 carbon, 10 to 35 cobalt, 0.2 to 1 chromium, 0.2 to 1 molybdenum, and 0.15 to 2 vanadium or other carbide former, with the remainder essentially iron except for the usual impurities. As is well known in the art, in larger sized components, materials such as boron, manganese and nickel can be added in usual amounts to increase hardenability without seriously affecting the other characteristics.

The materials are heat treated in an appropriate manner to essentially dissolve all of the metal carbide, cooled to allow transformation to a predominently bainitic structure and tempered in a manner suitable to obtain a good combination of magnetic and mechanical properties. Generally speaking, the materials are heated at a temperature of from 1700 F. to 2000 'F. for about 5 to 25 hours in a well-known manner, and then quenched as in water. The tempering, as is the prior heat treatment, is essentially of a time-temperature nature and can be carried out at temperatures varying from about 1000 F. to about 1400 F. for from about 1 to 64 hours, preferably 1250 F. to 1400 F. for from about 16 to 64 hours. Variations in the above heat treatments will occur to those skilled in the art.

Those features of the invention which are believed to be novel are set forth with particularity in the claims appended hereto. The invention will, however, be better understood and further advantages and objects thereof appreciated from a consideration of the following description.

The following examples illustrate the practice of the present invention, it being realized that they are to be taken as exemplary only. All parts are in percent by weight. The remainder of each alloy is essentially iron except for the usual impurities. The materials shown in the examples of Table I below were heat treated at 1920 F. for 16 hours in a nitrogen atmosphere, water quenched and four samples tempered for 64 hours at 1400 F. Four other samples were tempered for 16 hours at 1256 F.

TABLE I 0 00 V Cr Mo Shown in Table II below are the room temperature, mechanical and magnetic properties of the materials of the invention.

TABLE II 0.2% q 0.02% Tensile yield yield Elonga- Reduction B (kllogauss) atstrength strength strength tion in area (k.p.s.1.) (k.p.s.i.) (k.p.s.i.) (percent) (percent) ca. 0e. 300 oe.

Tempered 16 hours at 1,256 F.:

Ex. 1 152. 8 137. 5 115. 0 20. 0 58. 6 15. 2 18. 4 21. 4 l4. 6 18. 4 21. 7 l4. 3 l7. 9 21. 4 14. l 17. 8 21. 3

*Broke prematurely during test.

Shown in Table III are the mechanical and magnetic properties of the materials of Table II, when tested at 1000 F. Also given are published data concerning various prior art alloys.

3. An alloy as in claim 1 consisting essentially of in percent by weight, carbon 0.22, cobalt 19.3, chromium 0.49, molybdenum 0.56, vanadium 0.94, with the remainder essentially iron.

TABLE I l 1 0.2% 0.02% Tensile yield yield Elonga- Reduction B (kilogauss) at strength strength strength tion in area (k.p.s.i.) (k.p.s.i.) (k.p.s.i.) (percent) (percent) 75 e. 150 00. 300 0e Tempered 16 hours at 1,256" F.:

Ex. l 102.5 06. 0 81. 4 22. 0 63. 2 15.6 18.1 10. EX. 2 130. 0 122. 0 08. 1 12.0 21. 1 15.0 17. 0 20.0 EX. 3 112. 5 101. 0 83. 0 17. 5 45. 5 14.6 17. 7 19. 7 EX. 4 119. 4 11 1. 4 82. 8 6. 5 14. 6 14. 2 17. 2 19. 0 Tempered 64 hours at 1.400 F;

Ex. 1 60. 5 63. 0 53. 8 25. 0 73. 4 18. 2 10. 6 20. 4 EX. 2 74. 2 64. 2 50. 1 27. 5 72. 5 l7. 3 19. 0 20. 0 EX. 3. 78. 2 60. 5 58. 0 20. 5 74. 2 17. 7 19. 7 20. 8 Ex. 4 93. 4 85. 4 72.3 26.0 62. 7 16. 6 1t). 0 21.0 Prior art alloys:

Hypereo 27 64. 6 50. 1 41. 7 12. 4 41. 3 21. 2 22. 2 H-ll 132. 7 07. 8 23. 8 69. 0 13. 0 14. 0 14. 7 Niveo 129. 0 03. 0 80. 0 22. 7 .45. 4 0. 5 10.8 11. 0 Ni maragiug steel 102. O 177. 0 15. 0 48. 0 0. 4 12. 5 14. 3

It will be noted that the combined mechanical and magnetic properties of the alloys of the present invention are much improved over the prior art alloys shown. Hyperco 27 of Westinghouse is a 27% cobalt-iron alloy, H-ll is a commercial 5% Cr-MO-V steel and is a typical prior art magnetic alloy presently used in rotating electrodynamic machinery components operating at elevated temperatures. Nivco (Westinghouse) contains about 72% cobalt, 23% nickel, 1.1% zirconium, 1.8% titanium, 0.2% aluminum, 1% iron, balance cobalt, while the 15% nickel maraging steel contains about 15% nickel, 9% cobalt, 5% molybdenum, 0.7% titanium, 0.7% aluminum, balance iron.

It will be appreciated from a consideration of Table III above that the alloys of the present invention are far and away superior to prior art materials for high temperature applications where both good magnetic and strength characteristics are required.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An alloy characterized by good high temperature, soft magnetic and strength properties consisting essentially of in percent by weight, carbon 0.05 to 0.6, cobalt 10 to 35, chromium 0.2 to 1.0, molybdenum 0.2 to 1.0, vanadium 0.15 to 2.0, with the remainder essentially iron.

2. An alloy as in claim 1 consisting essentially of in percent by weight, carbon 0.11, cobalt 20.3, chromium 0.48, molybdenum 0.57, vanadium 0.48, with the remainder essentially iron.

4. An alloy as in claim 1 consisting essentially of in percent by weight, carbon 0.11, cobalt 29.8, chromium 0.45, molybdenum 0.50, vanadium 0.45, with the remainder essentially iron.

5. An alloy as in claim 1 consisting essentially of in percent by weight, carbon 0.23, cobalt 29.4, chromium 0.45, molybdenum 0.50, vanadium 0.91, with the remainder essentially iron.

6. An alloy characterized by good high temperature, soft magnetic and strength properties consisting essentially of, in percent by weight, carbon 0.05 to 0.6, cobalt 10 to 35, chromium 0.2 to 1.0, molybdenum 0.2 to 1.0, 0.15 to 2.0 of a metal selected from the group consisting of vanadium, niobium, titanium or tantalum, with the remainder essentially iron.

References Cited UNITED STATES PATENTS 1,338,133 4/1920 Honda -l26H 2,130,822 9/1938 Welch 75---126H 2,590,835 4/1952 Kirkby 75-l26H 2,848,323 8/1958 Harris 75126E HYLAND BIZOT, Primary Examiner U.S. Cl. X.R.

75-126F, 126G, 126H 

